python 的小技巧之统计list里面元素的个数

一般写法
def  count_list(std:list,tongji):
    i=0
    for item in std:
        if item==tongji:
            i+=1
    print(i)
if __name__=='__main__':
    lists=[1,2,3,4,5,1,2,3,4,5,2,2,2,3,4]
    count_list(std=lists,tongji=2)

新写法， python 3.5 之后
def  count_list(std:list,tongji):
    from collections import Counter
    name=Counter()
    for  num in std:
        name[num]+=1
    print(name[tongji])
if __name__=='__main__':
    lists=[1,2,3,4,5,1,2,3,4,5,2,2,2,3,4]
    count_list(std=lists,tongji=2)

少了一个if判断，而且 一次可以获取列表所有元素的个数

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